Heretofore, unless the internal portion of a molded article contained regular surfaces, that is, surfaces wherein a core could be readily removed after the molding of an article, special molding techniques were required. One method utilized to mold an article having an irregular internal surface was the "lost core" method wherein metal or salt was formed in the same shape as the desired internal passage or irregular surface. The article was then molded around the "lost core". To remove the irregular internal core, the metal or salt was generally melted or dissolved by utilizing various solvents and/or heat. This process destroyed the core.
A second method is the epoxy-sand matrix method wherein a rigid epoxy-sand matrix core is utilized to form the irregular internal shape. After the article was molded or cast, the core was destroyed and removed from the article.
U.S. Pat. No. 2,569,935 to Leguillon, et al, relates to the manufacture of composite articles having a fabricated portion of fabric, cords, and the like, and a body of a rubber-like material bonded thereto. An expansible bag is utilized as a core in the interior portion of a mold so that a tire can be molded thereabout. The inflated bag supports the tire during molding, after which it is deflated and the tire removed.
U.S. Pat. No. 3,719,735 to Valyi relates to a method for pressure molding a parison which is subsequently blow molded. A relatively thin sleeve of plastic corresponding to the shape of the blow core is placed over the blow core prior to molding the parison therearound to insulate the blow core from the temperature of the molten plastic so that a blow valve is protected from clogging and the blow core is protected from erosion during the molding step.
U.S. Pat. No. 3,929,954 to Valyli relates to a method for the production of injected blow molded containers having a preformed inner lining which is applied to the core of the injection molding tool without immediately direct contact with the heated portions of the core.
U.S. Pat. No. 3,991,146 to Barrie relates to encapsulating an insert in plastic by injection molding with one face of the insert bearing against the mold thus supporting the insert against movement during injection and with subsequent relative movement between the insert and the supporting mold face to allow the injected material to float around the face of the insert.
U.S. Pat. No. 4,289,817 to Valyi relates to lined articles having an outer plastic layer of transparent or translucent plastic and a decorated inner plastic layer so that the decoration is visible through the outer layer. The article is prepared by decorating a plastic liner and molding a transparent or translucent plastic around the decorated liner.
U.S. Pat. No. 4,314,964 to Ferrary relates to a method of injection molding an article wherein an inflatable inner sleeve is utilized to form the internal shape of the molded article.
U.S. Pat. No. 4,352,772 to Bezner relates to the plastic injection molding of a manifold in which a first part is made by an extrusion followed by the injection molding of the plastic over the extrusion. A core is used and defines a shape of the internal space of the final manifold.
The above patents do not disclose the molding of an article having an irregular internal surface or passage by utilizing a polymer, preferably a thermoplastic preform or the utilization of a generally incompressible material within the preform during molding of the article.